April 2011
Volume 52, Issue 14
Free
ARVO Annual Meeting Abstract  |   April 2011
Reflectance Decrease Prior to Thinning of Retinal Nerve Fiber Layer in Glaucomatous Retinas
Author Affiliations & Notes
  • Ye Zhou
    Biomedical Engineering Department, College of Engineering, University of Miami, Miami, Florida
  • Xiangrun Huang
    Biomedical Engineering Department, College of Engineering, University of Miami, Miami, Florida
    Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, Miami, Florida
  • Wei Kong
    Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, Miami, Florida
  • Robert W. Knighton
    Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, Miami, Florida
  • Footnotes
    Commercial Relationships  Ye Zhou, None; Xiangrun Huang, None; Wei Kong, None; Robert W. Knighton, None
  • Footnotes
    Support  NIH grant nos. R01-EY019084, Center Grant P30-EY014801, American Health Assistance Foundation G2008-033 and an unrestricted grant to the University of Miami from Research to Prevent Blindness, Inc.
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 2443. doi:
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    • Get Citation

      Ye Zhou, Xiangrun Huang, Wei Kong, Robert W. Knighton; Reflectance Decrease Prior to Thinning of Retinal Nerve Fiber Layer in Glaucomatous Retinas. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2443.

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Abstract
 
Purpose:
 

Retinal nerve fiber layer (RNFL) consists of axons of retinal ganglion cells. Because glaucoma damages these axons, RNFL thickness, such as measured with OCT, is often used in clinic assessment of this damage. We have shown that glaucomatous damage alters these cylindrical structures before changes of RNFL thickness. In this study, we demonstrated that RNFL reflectance decreased prior to thinning of the RNFL and occurred first near the optic nerve head (ONH).

 
Methods:
 

A rat model of glaucoma with laser photocoagulation of trabecular meshwork was used. Reflectance of RNFL in an isolated retina was measured at wavelengths of 400 - 830 nm. After reflectance measurements, the retina was stained with antibodies to label the axonal cytoskeleton. RNFL thickness (T) was measured by confocal fluorescence imaging. Reflectance relative to a diffuse white surface was calculated for bundle areas located at radii of 0.45, 0.8 and 1.0 mm from the ONH center. Because RNFL reflectance is very directional and wavelength dependent, bundles with peak reflectance and similar scattering geometry were selected and the mean reflectance (R) at different wavelength ranges was calculated. The reflectance ratio (P=R/T) was used for comparison. For glaucomatous eyes, only those bundles with no apparent structural damage were used.

 
Results:
 

Eighteen bundles of 10 control retinas and 21 bundles of 10 treated retinas were examined. Bundle thickness of both groups at each radius was not significantly different (p>0.2). However, in each wavelength range the reflectance ratio at 0.45-mm radius decreased significantly in the treated group, while the ratios were similar at the radii of 0.8 and 1.0 mm.  

 
Conclusions:
 

Elevation of intraocular pressure causes decrease of the RNFL reflectance that precedes change of RNFL thickness. The change may occur first near the ONH. The results suggest that decrease of RNFL reflectance near the ONH is an early sign of glaucomatous damage.

 
Keywords: nerve fiber layer • optical properties • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) 
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